High molecular weight polyesters are well known to those skilled in the art.
However, a major short-coming in the use of such polyesters in foamed compositions is their normally highly flammable nature. The flammability of polyesters has been reduced by using halogen-, phosphorus- or nitrogen-containing additives, and such compositions are described in various patents and publications. Flame retarded foamed polyester compositions are desired for many fields of use such as in home construction, automobile and aircraft manufacture, packaging, electrical equipment and the like.
With particular reference to polyesters of the poly(alkylene dicarboxylate) family and related copolyesters, it has been difficult to adequately render such materials flame retardant without sacrificing their inherent, superior properties.
It has now been discovered that if carefully selected families of polycarbonate resins are added to the normally flammable polyesters, alone or in further combination with selected groups of other such polycarbonate resins, there will be provided highly efficiently flame retardant polyester compositions, without any need for reinforcement, yet without modification of physical properties to the extent that they are rendered unuseable for structural applications.
By way of illustration, the addition of a compatible aromatic polycarbonate additive or additives of the type to be described hereinafter, provides compositions which are flame retardant to the point where they meet stringent Underwriter's Laboratory requirements for self-extinguishing compositions.
Moreover, the direct combustibilities of such compositions, as measured in the Oxygen Index Test according to ASTM standard method D-2863, are less than those of controls rendered flame retardant by prior art methods.
It is, accordingly, a principal object of this invention to provide a family of foamable flame-retardant polyester compositions.
Other objects and advantages of the invention will become apparent from the following detailed description.